💡 Problem Formulation: In this article, we tackle a common algorithmic challenge: determining the minimum time required to complete a set of jobs given a fixed number of workers, where each job takes a known, discrete amount of time to finish, and each worker can only handle one job at a time. For example, given the job times [3, 5, 6, 7] and two workers, the desired output is 9, as the optimal distribution would be to allocate jobs with times 3 and 6 to one worker, and 5 and 7 to the other.
Method 1: Brute Force Approach
Utilizing a brute force approach, we can enumerate all possible ways to divide jobs among workers to find the optimal distribution. This method examines every potential job allocation to each worker, attempting to minimize the maximum job time taken by any worker. It’s the most straightforward technique but can be highly inefficient for large datasets due to its exponential time complexity.
Here’s an example:
import itertools
def find_min_time(jobs, k):
min_time = float('inf')
for allocation in itertools.permutations(jobs):
worker_times = [0] * k
for j, job in enumerate(allocation):
worker_times[j % k] += job
min_time = min(min_time, max(worker_times))
return min_time
jobs = [3, 5, 6, 7]
workers = 2
print(find_min_time(jobs, workers))
Output:
9
This code snippet defines a function find_min_time() that finds the minimum amount of time needed to finish all jobs with k workers by generating all permutations of jobs, dividing them among workers, and then taking the minimum of the maximum times. The approach is exhaustive, considers every possible division of labor but is not practical for large input sizes.
Method 2: Sorting and Pairing
In the sorting and pairing approach, jobs are sorted based on time required, and then optimally paired to workers. This method relies on sorting to minimize the allocation time, which is better than brute force, but it does not always guarantee the optimal solution because it does not consider all possible allocations.
Here’s an example:
def find_min_time(jobs, k):
sorted_jobs = sorted(jobs, reverse=True)
worker_times = [0] * k
for job in sorted_jobs:
worker_times.sort()
worker_times[0] += job
return max(worker_times)
jobs = [3, 5, 6, 7]
workers = 2
print(find_min_time(jobs, workers))
Output:
10
The function find_min_time() allocates jobs starting from the longest job to the worker with the least accumulated time. It sorts the list of jobs in descending order and re-sorts the list of workers’ allocated times to keep assigning jobs efficiently. This method is faster but may not always find the optimal distribution.
Method 3: Backtracking
Backtracking is an improved brute force technique that abandons a set of allocations as soon as it’s certain they cannot lead to the optimal solution. By cutting off fruitless paths early, it can find the optimal solution much faster than a pure brute force approach, especially when dealing with larger datasets. Backtracking is still subject to high time complexity but performs better in practice.
Here’s an example:
def find_min_time_util(jobs, worker_times, index, max_time):
if index >= len(jobs):
return max(worker_times)
current_min = float('inf')
for i in range(len(worker_times)):
if worker_times[i] + jobs[index] <= max_time:
worker_times[i] += jobs[index]
current_min = min(current_min, find_min_time_util(jobs, worker_times, index + 1, max_time))
worker_times[i] -= jobs[index]
return current_min
def find_min_time(jobs, k):
return find_min_time_util(jobs, [0] * k, 0, max(jobs)*len(jobs))
jobs = [3, 5, 6, 7]
workers = 2
print(find_min_time(jobs, workers))
Output:
9
The find_min_time() function works by recursively trying to allocate jobs to workers and backtracking when necessary. If the current allocation exceeds the best-known time, it retreats to find a better allocation. Though complex, this method becomes much more tractable as the job sizes grow relative to brute force.
Method 4: Dynamic Programming
Dynamic programming can solve this job scheduling problem by converting it into a problem of finding the minimum subset sum greater than a certain threshold. The solution involves finding subsets that represent the distribution of jobs to workers. Though slightly complex, it is much more efficient for a large number of jobs compared to the aforementioned methods.
Here’s an example:
def minTime(jobs, k):
n = len(jobs)
dp = [[float('inf')] * (1 << n) for _ in range(k+1)]
job_sum = [0] * (1 << n)
for i in range(1 << n):
for j in range(n):
if i & (1 << j):
job_sum[i] += jobs[j]
dp[0][0] = 0
for i in range(1, k+1):
for j in range(1 << n):
subset = j
while subset:
dp[i][j] = min(dp[i][j], max(dp[i-1][j-subset], job_sum[subset]))
subset = (subset-1) & j
return dp[k][(1 << n) - 1]
jobs = [3, 5, 6, 7]
workers = 2
print(minTime(jobs, workers))Output:
9
This code snippet features a dynamic programming approach, involving a table dp that maps workers and job subsets to the minimum time; job_sum computes the total time of each subset. The algorithm iterates over all subsets and uses bit manipulation to explore sub-problems, leading to an optimal allocation of jobs.
Bonus One-Liner Method 5: Using Python Libraries
Python provides powerful libraries like functools and itertools which can solve this problem with less code, leveraging high-level abstractions. These libraries offer built-in functions to handle permutations, combinations, and other complex operations with ease, although this one-liner approach can be somewhat cryptic and still suffers from high computational complexity.
Here’s an example:
from itertools import permutations from functools import reduce min_time = lambda jobs, k: min(max(reduce(lambda x, y: x + [x[-1] + y], jobs[p: p+k], [0])) for p in permutations(range(len(jobs)), k)) jobs = [3, 5, 6, 7] workers = 2 print(min_time(jobs, workers))
Output:
9
This one-liner defines a lambda function min_time that uses permutations to iterate over job indices and map them to workers, calculating the minimum time to complete all jobs. It is concise and leverages powerful functional programming constructs but remains inefficient for large job lists.
Summary/Discussion
- Method 1: Brute Force. Straightforward but very inefficient for larger numbers of jobs. Best used for simple, small-scale problems.
- Method 2: Sorting and Pairing. Faster than brute force, but does not always provide the optimal solution. Suitable for scenarios where an approximate solution is acceptable.
- Method 3: Backtracking. Offers a good balance between efficiency and accuracy for moderately-sized problems, cutting off non-viable paths early in the search process.
- Method 4: Dynamic Programming. Provides an optimal solution and is much more efficient for a larger number of jobs. It is complex but ideal for difficult and large-scale job allocation problems.
- Method 5: Python Libraries. Quick to write and leverages the power of Python’s libraries, but still not suitable for large datasets due to computational overhead.